Block of T-338A-CFTR by internal and external SCN− ions. (A) Example single channel currents for T-338A-CFTR, recorded from inside out patches at membrane potentials of +50 mV or −50 mV, under control conditions and in the presence of 10 mM SCN− in the intracellular or extracellular solution, as indicated. (B) Mean unitary current-voltage relationships for T-338A-CFTR, under control conditions (○) and in the presence of 10 mM SCN− (•) in the intracellular (left) or extracellular (right) solution. Mean of data from 3–10 patches. (C) Fractional unitary current remaining in the presence of 10 mM intracellular SCN− for wild-type (•) and T-338A (○). (D) Fractional unitary current remaining in the presence of 10 mM extracellular SCN− for wild-type (•) and T-338A (○). In C and D, data for wild-type are taken from Linsdell (13) under identical ionic conditions.